1. Field of the Invention
The present invention relates to a relief valve, more particularly, to a relief valve that allows a valve seating sound to be reduced and the design of a return spring to be made simple.
2. Background Art
As shown in FIG. 3, the conventional relief valve 01 includes a cylindrical case 02 with one side thereof (or the left side shown in the figure) communicated with a fluid pressure source; a relief piston 03 accommodated in the cylindrical case 02 in such a way that the piston 03 can be sled with a high degree of freedom; a return spring 04 for pressing the relief piston 03 against the fluid-pressure source; and a stopper 015 for seating the relief piston 03.
Relief holes 05 are bored through walls of the cylindrical case 02. When the relief piston 03 retreats due to an increase in pressure generated by the fluid-pressure source, the relief holes 05 are communicated with the fluid-pressure source, allowing the relief valve 01 to get rid of the increase in pressure generated by the fluid-pressure source. Reference numeral 013 denotes a guide cover for orienting an escaping pressed fluid in one direction.
Due to the conventional relief valve 01 having the configuration described above, after the relief valve 01 gets rid of an increase in pressure generated by the fluid-pressure source, the relief piston 03 returns from a retreat position to a seat position, generating a seating sound due to a collision with the stopper 015. In some cases, this seating sound results in noise.
In addition, because the return spring 04 is accommodated in a small space inside the cylindrical case 02, the setting of an anticipated relief pressure and the reduction of the valve seating sound are not achieved readily.
It is thus an object of the present invention to provide a relief valve capable of reducing a seating sound of the relief piston (or the relief valve element).
A further object of the present invention is to provide a relief valve where seating of a relief piston is achieved with reduced noise generation.
Another object of the present invention is to provide a relief valve where the return spring thereof may be designed with ease.
These and other objects of the present invention are solved by providing a relief valve having a cylindrical case with one side thereof communicated with a fluid-pressure source; a relief piston accommodated in the cylindrical case in such a way that the piston can be sled with a high degree of freedom; and a return spring for pressing the relief piston against the fluid-pressure source, wherein a relief hole bored through a wall of the cylindrical case is communicated with the fluid-pressure source when the relief piston retreats due to an increase in pressure generated by the fluid-pressure source, and wherein the relief-valve includes a damper chamber, provided on a rear-surface side of the relief piston, communicated with the fluid-pressure source through an orifice and used for displaying a buffer action against a movement of the relief piston.
The configuration of the present invention includes a damper chamber, provided on a rear-surface side of the relief piston, communicated with the fluid-pressure source through an orifice and used for displaying a buffer action against an operation of the relief piston. As a result, when the relief piston returns from a retreat position to a seat position after the relief valve relieves an increase in pressure generated by the fluid-pressure source, the return movement is slowed down, reducing the magnitude of a seating sound generated by a collision of the piston with the stopper, hence, causing no noise.
In addition, since part of a spring load of the return spring holding the relief valve at the seat position is borne by the buffer action of the damper chamber, the spring load of the return spring can be assumed to have a small value in comparison with the conventional relief valve. Thus, a small return spring can be employed. As a result, the design of the return spring accommodated in a small space inside the cylindrical case can be made simple.
Moreover, since the retreat and return movements of the relief piston-are slowed down, variations in pressure generated by the liquid-pressure source decrease, thus, smoothing the operation of equipment, such as various kinds of hydraulic equipment.
Furthermore, the relief piston includes a central separation wall and first and second sleeves created on both sides of the central separation wall, thereby sandwiching the central separation wall. The first sleeve is accommodated at one end of the cylindrical case in such a way that the first sleeve can be sled with a high degree of freedom, and the second sleeve is accommodated at the other end of the cylindrical case. An orifice is bored through the separation wall and a sleeve hole is bored through the first sleeve. The damper chamber comprises the separation wall, the second sleeve and a stationary damper piston fitted into the second sleeve in such a way that the damper piston can be sled with a high degree of freedom inside the second sleeve relatively to the second sleeve.
As a result, in the relief piston, the separation wall and the first sleeve having a sleeve hole bored through it function as an element of the relieve valve whereas, at the same time, the separation wall with an orifice bored through it and the second sleeve are utilized as elements constituting the damper chamber. Thus, the damper chamber can be formed with ease and the structure of the damper chamber can be made simple.
In addition, the relief piston includes a central separation wall and first and second sleeves created on both sides of the central separation wall, thereby sandwiching the central separation wall. The first sleeve is accommodated at one end of the cylindrical case in such a way that the first sleeve can be sled with a high degree of freedom, and the second sleeve is accommodated at the other end of the cylindrical case. An orifice is bored through the separation wall and a sleeve hole is bored through the first sleeve. The damper chamber includes the separation wall, the second sleeve and a stationary damper-bottom cylinder engaged with the second sleeve, such that the damper-bottom cylinder can be sled with a high degree of freedom inside the second sleeve relative to the second sleeve.
As a result, in the relief piston, the separation wall and the first sleeve having a sleeve hole bored through it function as an element of the relieve valve whereas, at the same time, the separation wall with an orifice bored through it and the second sleeve are utilized as elements constituting the damper chamber. Thus, the damper chamber can be formed with ease and the structure of the damper chamber can be made simple.
Moreover, a damper-bottom cylinder is used in the creation of a damper chamber as a member which serves as a partner of the second sleeve and is engaged with the second sleeve in such a way that the damper-bottom cylinder can be sled with a high degree of freedom inside the second sleeve relatively to the second sleeve. Thus, the damper chamber can be created more easily and the weight of the relieve valve can be reduced.
Furthermore, a stair is created between the ends of the cylindrical case, and an outermost-circumferential flange of the separation wall of the relief piston is seated on the stair.
As a result, since a seat surface of the relief piston can be created by utilizing the stair formed by virtue of a difference in internal diameter between the ends of the cylindrical case, which is created to have a relatively large diameter and to accommodate the return piston, the seat surface can be formed with ease.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.